1. Field of the Invention
The present invention relates to an optical part, a lens barrel, and a camera, and more particularly relates to an optical part, lens barrel, and camera having a light shielding portion for blocking out harmful light.
2. Description of the Related Art
Ghost, flare, and other such problems that adversely affect the formation of an image sometimes occur in cameras and other such optical devices. When strong light is incident on an imaging optical system, part of the incident light is reflected by the lens surface in the imaging optical system, and this reflected light (harmful light) forms a false image, and this is what leads to ghost and flare.
Examples of how the generation of such harmful light can be suppressed include a method in which a thin, annular light shielding sheet is provided to the non-effective optical area of a lens, and a method in which a light shielding treatment is performed on the non-effective optical area of a lens.
The light shielding treatment of a lens is generally accomplished by inking, printing, or the like. Inking is a method in which the surface of a lens is coated with ink with a brush or the like. Examples of printing methods include screen printing and pad printing. These printing methods are disclosed, for example, in Japanese Laid-Open Utility Model Applications H4-109734 and H1-128328 and Japanese Laid-Open Patent Applications 2003-57721 and 2002-82370.
Optical devices need to have an overall compact size to make them more portable. More specifically, there is a need for a reduction in size of the lens barrel, which is considered to be a major factor in obtaining a smaller overall size.
As the size of a lens barrel is reduced, it becomes necessary to reduce the diameter of the lenses included in the imaging optical system. In this case, the amount of light passing through the lenses remains the same even though the lens barrel is made smaller. Consequently, when the diameter of a lens is decreased, illumination intensity (the amount of light per unit of surface area) on the lens increases. When a light shielding sheet is used, however, the distance between lenses cannot be shortened, and furthermore space must be provided to fix the light shielding sheet, which impedes efforts at reducing the size of the lens barrel.
Meanwhile, when harmful light is blocked not just by a light shielding sheet, but also by inking, there may be cases when the harmful light cannot be effectively blocked. The reason for this is that with inking, there tends to be variance in the coating film thickness, and the light shielding film is very thin, and that the original purpose of this ink is to reduce scattered reflection at the edges of the lens (the outer peripheral part of the lens), and the ink does not have high light shielding performance. Therefore, even though a reduction in lens barrel size may be achieved, there are cases when harmful light cannot be blocked with inking alone, and the optical performance of the optical system deteriorates.
Thus, there has been a need with conventional optical parts both to enhance optical performance and to reduce size.